From mapping to manipulation: 3D insights into dielectrophoresis and electrokinetics for advanced sorting toward colloidal memory applications

The precise manipulation of nanoscale particles is essential for advancing applications in colloidal selfassembly, targeted sorting, and emerging paradigms such as colloidal memory. Here, we present a high-speed multiplane 3D imaging platform that enables direct visualization and quantification of dielectrophoretic (DEP) forces and electrokinetic flows acting on individual nanoparticles in real time. Using 200 nm dye-doped polystyrene particles, we map both positive and negative DEP regimes, capturing spatial force distributions with sub-50 nm axial resolution and frame rates exceeding 100 fps. Our approach reveals distinct particle behaviors across frequency regimes, including trapping near electrodes under positive DEP and levitation above the surface under negative DEP. In addition, we characterize electrokinetic flow fields in 3D, which play a critical role at higher voltages. This methodology provides a robust experimental framework for investigating DEP manipulation schemes, validating theoretical models, and selectively addressing particle mixtures, a key requirement for future molecular machines and frequency-controlled colloidal memory systems.